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Cosmic collisions spin stellar corpses into gold

By Lisa Grossman

A BRIEF but brilliant flash in the distant universe suggests that smacking two dead stars together can create heavy elements in vast amounts – including 10 moon masses’ worth of gold.

After the big bang, the universe contained only hydrogen, helium and lithium. Elements lighter than iron are built up in the cores of massive stars and released when they die. It had been thought that heavier elements are forged during supernova explosions, but computer simulations of the process didn’t always produce the proportions of these elements seen in nature.

Some researchers instead suggested that heavy elements could be created more efficiently during the collision of two neutron stars, the dense balls of mostly neutrons left over after a supernova.

On 3 June, NASA’s Swift satellite caught a short burst of energetic gamma rays coming from a galaxy 3.9 billion light years away. One of the most likely culprits is a pair of neutron stars colliding to form a black hole.

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A team led by Edo Berger of the Harvard Smithsonian Center for Astrophysics in Cambridge, Massachusetts, looked at data from the Hubble Space Telescope showing the same spot in the sky nine days after the burst. They saw an afterglow in long-wavelength infrared light, a signature of radioactive decay (arxiv.org/abs/1306.3960). A second team led by Nial Tanvir at the University of Leicester, UK, also looked at the Hubble data and detected the same infrared glow (arxiv.org/abs/1306.4971).

Based on the brightness of the afterglow, Berger’s team estimates that 3 per cent of the neutron stars’ combined material was tossed outwards in the collision and escaped the black hole. The ejected neutrons that produced radioactive elements should also have created huge amounts of stable, heavy elements such as gold and platinum. The team now argues that neutron star smashes can account for almost all of our heavy elements.

This article appeared in print under the headline “Collisions spin stellar corpses into gold”